Planktic Foraminiferal Test Research Articles

Orbital timescale CaCO3 burial and dissolution changes off the Chilean margin in the subantarctic Pacific over the past 140 kyr

Calcium carbonate (CaCO3) dissolution at the Southern Ocean seafloor has hypothetically contributed to lowering the atmospheric carbon dioxide concentration by increasing ocean alkalinity during glacial periods. We present new CaCO3 burial and dissolution records from two sediment cores obtained off the Chilean margin in the subantarctic SE Pacific and covering the past 140 kyr since Marine Isotope Stage (MIS) 6. These records include CaCO3 contents and mass accumulation rates, and microfossil-based analysis results, including fragmentation ratios, sieve-based weights (SBWs), and ultrastructural observations of planktic foraminiferal tests. Our bulk CaCO3-based analyses and Globorotalia inflata SBWs revealed three major CaCO3 dissolution events during colder stages of MIS 5d and 5b and at the MIS 5/4 boundary that are traceable events in the eastern South Pacific along the Chilean margin and in the Drake Passage. Furthermore, CaCO3 burial exhibited pronounced glacial/interglacial fluctuations, with almost no burial during glacials (MIS 6, 4, 3, and 2) and recovery during interglacials (MIS 5e and 1) and early glacials (MIS 5d–a). This pattern agrees with previous observations over a wide area of the Southern Ocean, except in the deep Cape Basin > 4600 m in the South Atlantic Ocean. Considering that our sites were located upstream of the Drake Passage, the Circumpolar Deep Water, which was influenced by carbon-rich Pacific Deep Water, likely propagated from the subantarctic eastern Pacific to the South Atlantic at least at depths of ~ 3000 to ~ 4000 m and decreased CaCO3 burial during glacials. These findings supported the importance of carbonate compensation in the Southern Ocean for the carbon cycle on the glacial/interglacial timescale.

INTRATEST TRACE ELEMENT VARIABILITY IN POLAR AND SUBPOLAR PLANKTIC FORAMINIFERA: INSIGHTS INTO VITAL EFFECTS, ONTOGENY, AND BIOMINERALIZATION PROCESSES

ABSTRACT To use planktic foraminiferal tests as paleoproxy substrates, it is necessary to delineate environmental versus biological controls on trace element incorporation. Here we utilize laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to explore interspecies, chamber-to-chamber, and intratest trace element (i.e., Mg, Na, Sr, Ba, Mn, Zn) variability in thickly-calcified specimens of the polar and subpolar planktic foraminifera Neogloboquadrina incompta, N. pachyderma, and Turborotalita quinqueloba collected from plankton tows in the Northern California Current. Among the study taxa, test Mg/Ca, Na/Ca, and Sr/Ca are likely dominantly controlled by depth habitat. The neogloboquadrinids record higher Ba/Ca and Mn/Ca and also show positive covariance between these elements, possibly due to calcifying in an oxygen-depleted marine snow microhabitat. Trace elements are found to be more enriched in the lamellar calcite than the outer chamber wall dominated by gametogenic crust. The data presented herein provide insight into potential vital effects, paleoproxy considerations, ontogeny, and biomineralization processes.

Mineralogy of Quaternary Sediments from the Valley of Vema Fracture Zone (Central Atlantic)

The content of sediment forming minerals in two cores from the eastern (ANS45-37) and western (ANS45-48) parts of the Vema transform fault valley is studied using the semi-quantitative XRD analysis of bulk powder sediment samples. The mineral composition of deep-sea sediments from the Amazone cone is also analyzed for comparison. It appeared that the average composition of the terrigenous component of both cores (according to prevailing quartz, secondary mica, plagioclase and potassium feldspar, as well as smectite, chlorite, kaolinite, illite) is quite similar and approximately corresponds to the composition of sediments from the Amazon cone. The ratio of four clay minerals suggests the supply of terrigenous material to the Amazon and Orinoco due to the erosion of the Andes and humid tropical weathering in the lower course of the rivers with further transportation of the suspended load to the ocean. This material was transported to the Vema transform valley due to the interplay between the gravity flows from the South American continental slope and the current of the Antarctic Bottom Water. Data on biogenic calcite (planktic foraminiferal tests, nannofossils) and opal A (radiolarians, sponge spicules) are obtained in addition. In the study area, several authigenic (diagenetic) minerals are identified. In particular, siderite and greigite are first found in the sediments from the Vema valley and Amazon cone, respectively.

Extreme Planktic Foraminiferal Dwarfism Across the ETM2 in the Tethys Realm in Response to Warming

AbstractPronounced warming negatively impacts ecosystem resilience in modern oceans. To offer a long‐term geological perspective of the calcareous plankton response to global warming, we present an integrated record, from two Tethyan sections (northeastern Italy), of the planktic foraminiferal and calcareous nannofossil response to the Eocene Thermal Maximum 2 hyperthermal (ETM2, ∼54 Ma). Our study reveals pronounced changes in assemblage composition and a striking dwarfing of planktic foraminiferal tests of up to 40% during the event, impacting both surface and deeper dwellers. The increased abundance of small placoliths among calcareous nannofossils is interpreted as community size reduction. Literature and our foraminiferal size data from Sites 1263 and 1209 (Atlantic and Pacific Oceans) highlights that the pronounced dwarfism is restricted to the Tethyan area. The ETM2 is characterized by warm sea surface temperatures as indicated by our δ18O data, but this warming is of global extent and cannot explain the unique dwarfism. Excluding evolutionary modifications, other potential drivers of dwarfism (eutrophication, deoxygenation, metabolic adaptation) cannot explain the exceptional dwarfism by themselves. The smallest sizes are in close temporal association with peaks in volcanic derived Hg/Th‐Hg/Rb recorded just before and at the ETM2 which could not have been brought into our sections through weathering. In contrast, size reductions are absent below and above the ETM2 at Hg peaks where δ18O data do not show warm conditions. We speculate that the local input of toxic metals from submarine volcanic emissions could have acted synergistically to warming, causing the unique dwarfism.

A new methodology for foraminifera extraction from cemented calcareous shelf sediments

Choosing the most conservative technique to extract unequivocally identifiable foraminiferal tests is crucial to avoid biases in sedimentary sequence dating and paleoenvironmental interpretations. However, for problematic samples containing heavily encrusted specimens, the concentration and isolation of microfossils might be challenging. In this work, we analyzed Early-Middle Pleistocene samples from the International Ocean Discovery Program (IODP) Site U1460, located on the southwestern Australian shelf platform, characterized by extensive early marine diagenesis. At this site, foraminiferal preservation varies between the glacial and interglacial phases. In particular, tests are highly encrusted in samples representing sea-level lowstands of glacials while exhibiting better preservation in samples corresponding to interglacials. As the application of previously established, very conservative preparation techniques (e.g., sieving technique, soaking in H2O2 solution and gentle sonication) did not produce satisfactory results, it was necessary to set up a new procedure for foraminifera isolation specifically for the cautious cleaning of cemented benthic and planktic foraminiferal tests. This new methodology combines the use of a freeze-dryer with repeated soakings in highly-diluted H2O2 solution to disaggregate the material. To evaluate the efficiency of our technique objectively, we considered the improvements obtained with our procedure on the worst-preserved samples of our record (corresponding to glacials) and the best-preserved (associated with interglacials). Despite being more time-consuming than other preparation techniques, this newly developed procedure produces excellent results in samples exhibiting a high level of encrustation for reliable quantitative studies and isotope analysis on foraminiferal assemblages. Our new methodology is highly conservative and thus preserving even delicate taxa.

Seasonal variation of fluxes of planktic foraminiferal tests collected by a time-series sediment trap in the central Bay of Bengal during three different years

Sediment trap samples from the southwestern Bay of Bengal were obtained at a water depth of about 900 m at sampling intervals of 17–27 days during three time periods (November 1988 to October 1989, December 1990 to October 1991, and January 1993 to October 1993). The planktic foraminifer abundances and assemblages of the samples were analyzed, and the factors governing the assemblages and their potential as indicators of climate and ocean processes in the sedimentary record were examined. We identified 28 species of planktic foraminifers in the samples, of which seven species accounted for more than 80% of each assemblage. The highest fluxes of planktic foraminifer tests were generally observed during the summer and winter monsoon seasons, and the lowest fluxes were observed during the intermonsoon seasons, especially from March to May. Periods of enhanced primary production during monsoons were accompanied by a sharp increase in the flux of Globigerina bulloides, whereas nutrient depletion in the surface ocean in spring led to subsurface small size plankton production and low planktic foraminifer test fluxes. The seasonality of foraminiferal assemblages and fluxes was controlled mainly by seasonal surface and subsurface primary production. The transition of abundant species from subsurface dwellers to surface ones throughout the monsoon season can be attributed to initial subsurface primary and secondary production being succeeded by enhanced surface production. The foraminiferal flux pattern differed among the three observation periods, especially in summer, because of interannual variation in the regional physical forces that induce nutrient replenishment at the surface. However, the consistent features of the flux pattern, with peaks during the monsoon seasons and minimal values in spring, suggest that our results reveal the essential, long-term flux pattern of planktic foraminifers in the southwestern Bay of Bengal.

Planktic foraminifera of the upper Barremian–Aptian black shale intervals from the Chaqiela section (Gamba, southern Tibet): Biostratigraphic and palaeoenvironmental implications

Marine sedimentary intervals of the upper Barremian–upper Aptian record the profound changes in global plate configurations and the ocean-climate system. Black shale lithofacies of the Lower Cretaceous crop out extensively in the Tethyan Himalaya region of southern Tibet, and in the Gamba area they are assigned to the Gambadongshan Formation. By using 3–5% hydrofluoric acid, well-preserved planktic foraminiferal tests have been recovered for the first time from black shales in the Chaqiela section of the Gambadongshan Formation. The detailed foraminiferal biostratigraphic work allowed recognition of four upper Barremian to upper Aptian planktic biozones: Hedbergella excelsa Interval Zone, Globigerinelloides ferreolensis Taxon-Range Zone, Hedbergella infracretacea Partial-Range Zone, and the Paraticinella rohri Taxon-Range Zone. Total organic carbon (TOC) and organic carbon isotope (δ13Corg) records were generated for the Chaqiela section. The C-isotope profile and the planktic foraminiferal data enable the identification of Oceanic Anoxic Event 1a (OAE 1a) at the lower part of the Globigerinelloides ferreolensis Taxon-Range Zone. Diagenetic processes, lower sea surface temperature, and the regional hydrologic cycle were probably the main factors for the development of OAE 1a in the Chaqiela section. The relatively higher δ13Corg values and smaller size of carbon isotopic fluctuations in the Chaqiela section may represent the local expression of OAE 1a in the Gamba area. A long-term negative δ13Corg excursion and a decreased trend of planktic foraminiferal abundance relative to benthic foraminifera, in the upper part of the Gambadongshan Formation may suggest a lower sea-level during the late Aptian.

Influence of the Latest Maastrichtian Warming Event on planktic foraminiferal assemblages and ocean carbonate saturation at Caravaca, Spain

A global warming episode in the Late Cretaceous, the Latest Maastrichtian Warming Event (LMWE), has been commonly linked to both the onset of massive Deccan Trap volcanism and the start of a planktic foraminiferal mass extinction prior to the Cretaceous/Paleogene boundary (KPB). The mechanisms that drove the LMWE are still under discussion, but radiometric dating of the onset of the main phase of the Deccan volcanism supports a temporal coincidence and permits a potential mechanistic link. Here we evaluate the planktic foraminiferal record, carbonate content and stable carbon and oxygen isotopes in the Caravaca section, in order to characterize paleoenvironmental change related to the LMWE. We identified negative δ13C and δ18O excursions in bulk carbonate from 66.35 to 66.14 Ma, i.e. ~310 to ~100 kyr before the KPB, which can be stratigraphically correlated to the LMWE and a major pulse of Deccan Traps volcanism. Within this warm interval, we identified high values in the fragmentation index of planktic foraminiferal tests, episodes of very high abundance of the low oxygen tolerant genus Heterohelix, a decrease of thermocline dwellers, dwarfing in Contusotruncana contusa tests, and an increase in the biserial morphotype of Pseudoguembelina hariaensis with elongated terminal chambers. However, the environmental disturbance during the LMWE did not cause changes in the planktic foraminiferal extinction rate. At Caravaca, the warming associated with LMWE was followed by a gradual cooling up to the KPB suggesting no extended interval of perturbed environments before the KPB extinction due to Deccan volcanism.

Three dimensional analysis of ontogenetic variation in fossil globorotaliiform planktic foraminiferal tests and its implications for ecology, life processes and functional morphology

Ontogenic trajectories recorded within the fossilized calcite tests of planktic foraminifera are significant for understanding their paleoecology and evolution. High-resolution 3-D imaging techniques enable quantitative measurement of test calcite and enclosed cavity volumes allowing a detailed characterization of the ontogenetic variations in the biomass to calcite ratio. Here we used micro-CT scanning to inspect ontogenetic variations among four globorotaliform planktic foraminiferal morphospecies from the late Miocene of International Ocean Discovery Program Site U1490 in the tropical Western Pacific. A conservative log-linear growth pattern is observed for all specimens. The proloculus size has an important control on the growth trajectory of the inspected specimens, and specimens with smaller proloculus volume generally have more chambers at the end of their life. The overall pattern of deviations from the log-linear growth trajectory among inspected specimens is well constrained, which varies between different groups in magnitude. The ontogenetic mean density, which is proposed here as an indicator of the degree of difficulty in producing positive buoyancy, shows a generally decreasing trend before the terminal stage in all specimens. We propose that the decreasing mean density (MD) as the test enlarges is an important adaption for planktic foraminifera to maintain an optimal habitat for nutrition and reproduction. The value of the mean density at the two-chambered stage exhibits a linear relationship with chamber volumes among inspected specimens with different habitats and different coiling forms, for which the ecological implications are explored.

Planktic Foraminiferal Test Size and Weight Response to the Late Pliocene Environment

AbstractAtmospheric carbon dioxide (pCO2atm) is impacting the ocean and marine organisms directly via changes in carbonate chemistry and indirectly via a range of changes in physical parameters most dominantly temperature. To assess potential impacts of climate change on carbonate production in the open ocean, we measured size and weight of planktic foraminifers during the late Pliocene at pCO2atm concentrations comparable to today and global temperatures 2 to 3 °C warmer. Size of all foraminifers was measured at Atlantic Ocean Deep Sea Drilling Project (DSDP) Site 610, Ocean Drilling Program (ODP) Site 999, and Integrated Ocean Drilling Program (IODP) Site U1313. Test size was smaller during the Pliocene than in modern assemblages under the same environmental conditions. During the cold marine isotope stage (MIS) M2, size increased at Site 999, potentially linked to intensified stratification of the surface ocean in response to the closure of the Central American Seaway. At Site U1313, test size tracks the warming throughout the late Pliocene. Size‐normalized weight (SNW) of Globigerina bulloides at Site U1313 decreased during warmer temperature intervals. SNW of Globigerinoides ruber (white) at Site 999 displays high‐frequency variability not correlated to temperature. Yet during the glacial period within MIS M2, test weight was higher during higher temperatures. Our results support studies in the modern ocean, which challenge the view that carbonate chemistry is the primary driver for calcification. To better understand processes driving changes in SNW, computer tomography was used to quantify calcite to volume ratios. During interglacial periods, lower calcite volume but higher test volume suggests less suitable conditions for calcification. As this signal is not evident in SNW, subtle changes in calcification might not be observed by the weight‐based method.

Do different extraction techniques impact planktic foraminiferal assemblages? An early Eocene case study

Abstract Here we report and compare results on planktic foraminiferal assemblages extracted with five disaggregation techniques: acetic acid, H2O2 at 10% and 25% concentration, neosteramina, and liquid N2. The aim is to estimate whether these laboratory procedures can affect the pristine assemblages or add secondary dissolution effects. We apply these five methods on three samples with different carbonate content from the early Eocene Tethyan Terche section (northeast Italy). For each method we assess: (1) the treatment effectiveness in relation to time required to successfully extract planktic foraminiferal tests and preservation; (2) the degree of dissolution through the analyses of three well-known dissolution proxies including the fragmentation index, the planktic benthic ratio and the weight percent coarse fraction; (3) changes in planktic foraminiferal assemblages through genera and species absolute abundances and the evaluation of multiple species diversity indices. Our data demonstrate that acetic acid and neosteramina treatments are the most effective methods as they represent the only ones capable in disaggregating the samples with higher CaCO3 content whereas liquid N2 revealed to be the best treatment to adopt for samples with low CaCO3 content. The best-preserved foraminiferal specimens derive from the acetic acid and neosteramina treatments. Nonetheless, the acetic acid along with H2O2 treatments, at both concentrations, can impact planktic foraminiferal assemblages affecting the diversity or species abundances. Dissolution of planktic foraminifera shows a complex relationship with the initial carbonate content (CaCO3%) of the samples and with the different dissolution susceptibility of the species that can differ according to the laboratory procedures.

Assessment of the Effect of Increasing Temperature On the Ecology and Assemblage Structure of Modern Planktic Foraminifers in the Caribbean and Surrounding Seas

Abstract Habitat patterns of subtropical and tropical planktic foraminifers in the Caribbean Sea were obtained from plankton samples collected in spring 2009 and 2013. The spatial distribution in surface waters (3.5 m water depth) and depth habitat patterns (surface to 400 m) of 33 species were compared with prevailing water-mass conditions (temperature, salinity, and chlorophyll-a concentration) and planktic foraminiferal test assemblages in surface sediments. Distribution patterns indicate a significant relationship with seawater temperature and trophic conditions. A reduction in standing stocks was observed close to the Orinoco River plume and in the Gulf of Paria, associated with high turbidity and concomitant low surface-water salinity. In contrast, a transient mesoscale patch of high chlorophyll concentration in the eastern Caribbean Sea was associated with higher standing stocks in near surface waters, including high abundances of Globigerinita glutinata and Neogloboquadrina dutertrei. Globorotalia truncatulinoides mainly lives close to the seasonal pycnocline and can be linked to winter conditions indicated by lower sea-surface temperatures (SSTs) of ∼20°C. Globigerinoides sacculifer and Globoturborotalita rubescens were associated with oligotrophic conditions in the pelagic Caribbean Sea during early spring and showed a synodic lunar reproduction cycle. The live assemblages in the water column from 2009 and 2013 were similar to those reported in earlier studies from the 1960s and 1990s and to assemblages of tests in the surface sediments. Minor differences in faunal proportions were attributed to seasonal variability and environmental differences at the local scale. An exception was the low relative abundance of Globigerinoides ruber in the Caribbean Sea in 2009 compared to surface sediment samples and plankton net samples collected in the 1960s and 1990s. Decreasing abundance of Gs. ruber white in the Caribbean Sea may be associated with increasing SSTs over past decades and changes in nutrient flux and primary production.

Understanding the Effects of Dissolution on the Mg/Ca Paleothermometer in Planktic Foraminifera: Evidence From a Novel Individual Foraminifera Method

AbstractIt is well documented that partial dissolution of planktic foraminiferal tests results in a reduction of Mg/Ca ratios, and hence of inferred calcification temperatures; however, traditional analysis techniques have made it difficult to identify the exact mechanism through which Mg is lost. Three hypotheses have been proposed as models for Mg loss for a given extent of dissolution: (1) a percent loss of Mg in individuals, (2) a molar loss of Mg in individuals, and (3) a loss of the highest‐Mg (warmest) individuals from a population. It is vital to better constrain these models as they have very different implications for Mg/Ca paleotemperature dissolution corrections. Here we use a novel individual foraminifera Mg/Ca method to examine the effects of dissolution on the Mg/Ca paleothermometer in three species of planktic foraminifera, Globigerinoides ruber, Neogloboquadrina dutertrei, and Pulleniatina obliquiloculata, from a depth transect of core tops on the Ontong Java Plateau in the western equatorial Pacific. With the exception of the most heavily dissolved population of P. obliquiloculata, our data best support a percent Mg loss model as indicated by the preservation of inferred temperature distribution shapes among the sampled populations and the close fit of the simulated percent Mg loss model to the observed data. Coupled with estimates for foraminiferal dissolution, identification of the percent Mg loss model will allow for more accurate dissolution corrections in Mg/Ca paleothermometry work.

Individual Migration Pathways of Modern Planktic Foraminifers: Chamber-by-Chamber Assessment of Stable Isotopes

Abstract. The stable carbon (δ13C) and oxygen isotopes (δ18O) of planktic foraminiferal tests have been widely used as proxies in paleoceanography and paleoclimatology. The ontogenetic isotopic profiles of foraminifers are also thought to record ecological information about species, such as changes in habitat depth and symbiotic relationships. However, isotopic profiles during “individual ontogeny” have rarely been examined. In this study, we report the ontogenetic isotopic information for three net-collected modern species, Globigerinoides sacculifer, Neogloboquadrina dutertrei, and Globorotalia inflata, together with several in situ oceanographic parameters of the water column in Sagami Bay, Japan (seawater temperature, salinity, nutrients, chlorophyll a content, δ13C of dissolved inorganic carbon [DIC], and δ18O of seawater). We examined the ontogenetic profiles of the foraminifers with chamber dissection and chamber-by-chamber analyses of δ13C and δ18O using a specially designed continuous-flow mass s...

The Impact of the Latest Danian Event on Planktic Foraminiferal Faunas at ODP Site 1210 (Shatsky Rise, Pacific Ocean).

The marine ecosystem has been severely disturbed by several transient paleoenvironmental events (<200 kyr duration) during the early Paleogene, of which the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma) was the most prominent. Over the last decade a number of similar events of Paleocene and Eocene age have been discovered. However, relatively little attention has been paid to pre-PETM events, such as the “Latest Danian Event” ("LDE", ~62.18 Ma), specifically from an open ocean perspective. Here we present new foraminiferal isotope (δ13C, δ18O) and faunal data from Ocean Drilling Program (ODP) Site 1210 at Shatsky Rise (Pacific Ocean) in order to reconstruct the prevailing paleoceanographic conditions. The studied five-meter-thick succession covers ~900 kyr and includes the 200-kyr-lasting LDE. All groups surface dwelling, subsurface dwelling and benthic foraminifera show a negative δ13C excursion of >0.6‰, similar in magnitude to the one previously reported from neighboring Site 1209 for benthic foraminifera. δ18O-inferred warming by 1.6 to 2.8°C (0.4–0.7‰ δ18O measured on benthic and planktic foraminiferal tests) of the entire water column accompanies the negative δ13C excursion. A well stratified upper ocean directly before and during the LDE is proposed based on the stable isotope gradients between surface and subsurface dwellers. The gradient is less well developed, but still enhanced after the event. Isotope data are supplemented by comprehensive planktic foraminiferal faunal analyses revealing a dominance of Morozovella species together with Parasubbotina species. Subsurface-dwelling Parasubbotina shows high abundances during the LDE tracing changes in the strength of the isotope gradients and, thus, may indicate optimal living conditions within a well stratified surface ocean for this taxon. In addition, distinct faunal changes are reported like the disappearance of Praemurica species right at the base of the LDE and the continuous replacement of M. praeangulata with M. angulata across the LDE.

Changes in East Asian summer monsoon precipitation during the Holocene deduced from a freshwater flux reconstruction of the Changjiang (Yangtze River) based on the oxygen isotope mass balance in the northern East China Sea

Abstract. The δ18O of seawater (δ18Ow), an indirect indicator of sea surface salinity (SSS), in the northern East China Sea (ECS) is reconstructed for the Holocene using paired analyses of Mg / Ca ratio and δ18O of planktic foraminiferal tests. According to modern observation, interannual variations in SSS during summer in the northern ECS are mainly controlled by the Changjiang (Yangtze River) discharge, which reflects summer rainfall in its drainage basin. Thus, changes in the summer SSS in the northern ECS are interpreted as reflecting variations in the East Asian summer monsoon (EASM) precipitation in the Changjiang Basin. This interpretation is confirmed by a strong relationship between the SSS in the northern ECS and the Changjiang discharge during the wet season (May–October) based on instrumental salinity records from 1951 to 2000. However, it is difficult to estimate absolute salinity values in the past with high accuracy, because the past salinity–δ18Ow regression slope, end member salinity, and δ18Ow values are not well understood. Here, we conduct δ18Ow mass-balance calculation to estimate the freshwater contribution to the surface water of the northern ECS during the last 7 kyr by assuming a simple mixing between two end members – the seawater and the Changjiang freshwater. The result indicates that there has been no gradual decreasing secular trend in the Changjiang freshwater flux from the middle Holocene to the present day, suggesting that summer insolation in the Northern Hemisphere does not regulate the EASM precipitation in the Changjiang Basin. Instead, internal feedback appears to have been more important during the Holocene. The absence of a decreasing trend in regional summer precipitation over the Changjiang Basin since the middle Holocene is contradictory to Chinese speleothems' δ18O records, suggesting that it is not possible to explain orbital changes in Chinese speleothems' δ18O during the Holocene by changes in summer precipitation, but that such changes are related to other factors such as changes in the moisture source.

Flux dynamics of planktic foraminiferal tests in the south-eastern Bay of Biscay (northeast Atlantic margin)

The temporal and water depth related dynamics of planktic foraminiferal fluxes in the south-eastern Bay of Biscay are discussed for a two year sampling period (June 2006–June 2008). Two sediment traps deployed at 800m and 1700m water depth at a mooring in 2000m of water depth, were analyzed for the flux of planktic foraminiferal species >150μm, in comparison with the total mass flux. Total flux of planktic foraminifera shows seasonal maxima in spring/early summer (>2000Ind.m−2d−1) and minima from late summer through winter (<10 Ind.m−2d−1). The flux of planktic foraminiferal tests in the intermediate to deep water column at the inner Bay of Biscay comprises an intermittent and regionally variable signal of seasonal surface water primary productivity. Significant lateral transport and flux of particles superimposed on the downward mass flux indicate a decoupling of fluxes between the 800-m and 1700-m traps. The 210Pb budget and the presence of certain benthic foraminiferal species in the midwater column prove that the lateral flux originated from the upper continental slope. Despite the temporal and vertical variations of the particulate flux, a well-defined seasonal flux signal can be deduced from the frequency of planktic foraminiferal species.

What happens when the ocean is overheated? The foraminiferal response across the Paleocene-Eocene Thermal Maximum at the Alamedilla section (Spain)

The global warming and major perturbation of the global carbon cycle that occurred during the Paleocene–Eocene Thermal Maximum (PETM) have been investigated in the lower bathyal–upper abyssal Alamedilla section (Spain). Geochemical anomalies and dramatic faunal changes (including the globally recognized extinction event of deep-sea benthic foraminifera and the rapid evolutionary turnover of planktic foraminifera and calcareous nannofossils) are associated with the PETM at Alamedilla. Biotic changes in the plankton and benthos indicate environmental instability ∼11–14 k.y. before the onset of carbon isotope excursion that marks the Paleocene/Eocene boundary. The reorganization of the planktic ecosystem points to warm and oligotrophic conditions in surface waters during the earliest Eocene, whereas faunal and geochemical data indicate that the extinctions of benthic foraminifera occurred over an interval with a high CaCO3 content and oxic conditions at the seafloor. The proliferation of disaster taxa ( Glomospira spp.) after the extinctions has been related to a potential source of isotopically light carbon in the western Tethys and North Atlantic. Significant changes in foraminiferal test size are documented across the PETM. We suggest that increased temperatures played an important role in benthic foraminiferal test size, increasing their metabolic rates and, consequently, their food requirements. Decreased planktic foraminiferal test size may be related to decreased nutrient availability or surface-water density. However, the differences in test size evolution among different species of both benthic and planktic foraminifera may be related to interspecific competition and ecological adaptations to direct or indirect consequences of the carbon addition during the PETM.

Planktic foraminiferal dissolution in the twilight zone

Abstract Calcite dissolution of planktic foraminifers that settle from the surface ocean to depths has been assessed using the weight/size relationship of tests and correlated to carbonate ion concentration ( [ CO 3 2 - ] ) of ambient sea water. Globigerina bulloides and Globigerinita glutinata were sampled from the North Atlantic and the Arabian Sea during different seasons (spring and fall and the monsoons, respectively). Test weight has been determined for single tests from narrow size classes ( 250 ± 8 μ m and 300 ± 7 μ m minimum test diameter). Initial test weight of both species in surface waters differs between regions and seasons. Weight loss of settling tests in the twilight zone between 100 and 1000 m water depths averaged 19%. Below the twilight zone (1000–2500 m) no weight loss occurs on average, and tests may even gain weight. Remineralization of settling planktic foraminiferal tests is most pronounced at maximum Δ CO 3 2 - . Accordingly, strong dissolution occurs in the twilight zone, at the depth of maximum decrease in Δ CO 3 2 - . It is assumed that dissolution of planktic foraminiferal calcite is caused by CO 3 2 - (under-) saturation inside the test, buffered by diffusive exchange of CO 3 2 - ions with the ambient sea water through the pores and aperture. Consequently, reconstruction of small-scale differences in seawater [ CO 3 2 - ] from test weight alone is not feasible and systematic correlation between test weight and Δ CO 3 2 - of the ambient sea water is statistically not significant. At constant [ CO 3 2 - ] , remineralization cannot be deduced from test weight, neither at high nor low CO 3 2 - saturation. In total, our data suggest that the global vertical planktic foraminiferal CaCO 3 flux is about 19% lower than calculated by Schiebel [2002. Planktic foraminiferal sedimentation and the marine calcite budget. Global Biogeochemical Cycles, 16 (4), 1065 [doi: 10.1029/2001GB001459]].

Two proximal, high-resolution records of foraminiferal fragmentation and their implications for changes in dissolution

Foraminiferal test fragmentation (150–250 μm-fraction) was studied at ∼3–6 kyr resolution in ODP Sites 925 and 926 on Ceara Rise (∼3000 and 3600 m water depth) from ∼6.34 to 5.0 Ma. This study investigates the driving forces behind changes in these two records and the potential of this proxy as an indicator of dissolution at depths above the lysocline. The records of fragmentation at both sites display variability concentrated in the precession band and the 125 and 96 kyr cycles of eccentricity superimposed on a low-frequency component, reminiscent of the 400 kyr cycle of eccentricity. Changes in terrigenous flux appear responsible for the manifestation of orbitally driven fragmentation susceptibility at the higher frequencies. The low-frequency trend is evident in both records of fragmentation, but marked by strong increases at the deeper site focusing on a dissolution-horizon suggestive of a supralysocline. Low coherence and shifting phases confound observed spectral power at 400 kyr, suggesting a mix of influences possibly unrelated to orbital variability. Proxies providing detail on changes in the sedimentary carbonate content reveal changes independent of the observed amplitude variability in the records of fragmentation. Low levels of carbonate accumulation and weight % sand up to 6.12 Ma suggest notable carbonate loss coincident with the first interval of increased fragmentation that may be influenced by a high surface to bottom δ 13 C gradient in addition to other factors. Changes in carbonate content at Site 929 on Ceara Rise (4356 m) reveal the same pattern of low-frequency carbonate dissolution as the records of fragmentation, thus identifying changes in depth of the carbonate compensation depth (CCD) as a driving force behind changes in carbonate preservation at shallower depths. Planktic foraminiferal test fragmentation appears to be a good proxy for pulsing of Antarctic Bottom Water (AABW) versus North Atlantic Deep Water (NADW) production at depths near and above the chemical lysocline (CL, ∼80% carbonate content).